Cushion stop for hydraulic cylinders



June 6, 1967 E. G. FREESE CUSHION STOP FOR HYDRAULIC CYLINDERS Filed Aug. '2, 1965 2 Sheets-Sheet 1 EVANS GLENN FREESE l NVENTOR.

ATTORNEY June 6, 1967 E. G. FREESE 3,323,422

CUSHION STOP FOR HYDRAULIC CYLT'NDFIRS Filed Aug. 2, 1965 2 Sheets-Sheet 2 F/G. 4 Y

EVANS GLENN FREESE INVENTOR ATTORNEY United States Patent 3,323,422 CUSHION STOP FOR HYDRAULIC CYLINDERS Evans Glenn Freese, Hutchinson, Kans, assignor to. The

Cessna Aircraft Company, Wichita, Kans., a corporation of Kansas Filed Aug. 2, 1965, Ser. No. 476,355 9 Claims. (Cl. 91405) ABSTRACT OF THE DISCLOSURE A piston carried valve for cushioning the stop of the piston by progressively restricting the outflow of fluid through a port in the cylinder, and capable of being moved transversely away from the port to afford free entry of pressure fluid into the cylinder to start the next cycle of piston movement.

This invention relates to reciprocating piston type hydraulically actuated motors, and more particularly to a structure for hydraulically cushioning the stop of a fast moving piston as it reaches the end of its stroke in either or both directions of travel.

It is a primary object of the invention to provide a structure for automatically and progressively decelerating the velocity of piston travel as the piston nears the end of its stroke, while relieving the cylinder of excessive internal pressure build up, by the gradual and progressive closing of a fluid discharge port, all without interfering with the entry of motive fluid through that same port when the control valve is shifted to introduce motive fluid into the cylinder to move the piston in the opposite direction.

It is a more specific object to provide a pressure unbalanced slide valve which is mounted to travel with the piston and its rod, which has a surface which is substantially complemental to the interior surface of the cylinder wall, and which surface is maintained in a position to cooperate with a side wall fluid port near the end of the cylinder to progressively restrict the flow of fluid outward through that port as a function of piston'movement, thus providing a fluid cushioned stop for the piston.

It is an additional object to provide a valve of the type mentioned which has limited transverse movement with respect to the inner surface of the cylinder (wall, which is resiliently urged into cylinder wall engagement for fluid metering cooperation'with the fluid port, as above described, yet which is movable laterally away from that port in response to pressure fluid introduced through the port, to thus allow free flow of fluid into the cylinder to force the piston to move toward the opposite end of its stroke.

It is a more specific object of this invention to provide a means for mounting a slide valve of the type mentioned on a piston, which mounting aflords limited transverse movement with respect to the longitudinal axes of the piston and its cylinder, yet which serves to maintain the orientation of the valve with respect to a fluid port in the cylinder wall as the piston reciprocates.

The invention, together with other objects which will become apparent, will be more clearly understood when the following description is read in connection with the accompanying drawings, in which:

FIG. 1 is a central longitudinal view through a piston and cylinder type motor with a slide valve embodying this invention mounted on the piston and rod assembly, the piston being located near thatoend of its stroke remote from the intake-discharge port, and the cylinder being shown fragrnentarily;

FIG. 2 is a side elevation of a part of the piston rotated from the FIG. 1 view, and shows details of construction;

FIG. 3 is a cross sectional view through the motor, and is taken in the plane indicated by the line 33 of FIG. 4;

FIG. 4 is a view similar to FIG. 1 except that the piston is illustrated as approaching the intake-discharge port 10- cated'near the opposite end of the cylinder;

FIG. 5 is a view similar to FIGS. 1 and 4, except that the piston is illustrated as having reached the limit of its permitted travel toward the ported end of the cylinder; and

FIG. 6 is an isometric view of a simplified slide valve embodying the invention.

Referring to FIG. 1, the piston and cylinder type motor illustrated includes a cylinder 10, a piston rod 11 having a shoulder 12, and a piston made up of concentric parts 22 and 27 which are held in position on the rod 11 by a nut 28.

The slide valve 14 shown in FIG. 1 is generally in the form of a sleeve, but has a reduced diameter internal shoulder 15 at one end, as shown. A rigid washer 13, of smaller outside diameter than the internal diameter of valve 14 seats on the rod shoulder 12 and on the valve shoulder 15 loosely, to allow lateral but not relative longitudinal movement for the valve.

In assembling the piston and valve structure shown, before it is inserted in the cylinder, the washer 13 is first seated on rod shoulder 12; the slide valve 14 is next slipped over the rod end with its shoulder 15 of reduced diameter adjacent washer 13; a valve movement guiding pin 17 has its reduced diameter end then slidably fitted into a drilled hole 16 in valve shoulder 15, with the opposite end of pin 17 abutting rod 11. The reduced end 18 .of a valve orienting pin 19 is next fitted with a coil spring 20, the spring is compressed against the inner surface of valve shoulder 15, and the opposite end of the pin is then slidably inserted into a drilled hole 21 in rod 11. Valve 14 should first be oriented so that pins 17 and 19 are substantially diametrically opposed. The described structure prevents relative rotational movement of the valve 14, but affords limited guided transverse movement of the valve along the common longitudinal axis of the pins 17 and 19, because the OD of the valve is less than the ID of cylinder 10.

Next, piston body 22 is slipped on the rod end, with its transverse diametral slot 23 (FIG. 2) receiving and forming a loose fitting housing for pins 17 and 19 and spring 20, and with its inner end surface 24 abutting the adjacent surface of washer 13. The depth of slot 23 is sufficient to permit this.

Piston body 22 carries annular cylinder wall packing 25, and a piston rod seal 26. Packing retainer 27 is then placed on rod 11 abutting piston body 22, and the entire assembly is secured together by a nut 28 threaded on the rod end. The entire described assembly is then inserted into the bore of cylinder 10, as shown.

It will be understood that if it is desired to cushion the stopping of the piston at both ends of its stroke it is only necessary to duplicate the described slide valve and mounting assembly at the opposite end of the piston 22.

Referring to FIG. 4, which shows the piston assembly approaching one end of its cylinder, it will be seen that the double acting cylinder shown is provided with a side wall fitting 29 which defines a combination motive fluid inlet and discharge port 30, the inner end opening of which is substantially flush with the inner surface of cylinder 10, and the outer end of which is connected to a suitable valve controlled conduit (not shown) which both supplies motive fluid to the cylinder and carries used fluid away from the cylinder.

While the flow area configuration of port 30 could be changed to provide for a more gradual metering of fluid by the slide valve 14, I prefer to provide the slide valve itself with a means for progressively decreasing the volume flow of fluid from the cylinder through the port 30 as the piston moves from its FIG. 4 position to its FIG. 5 position. This can be accomplished by an elongated external slot or groove 35 of a desired constant width and a depth which gradually decrcases from that end of the valve nearest port 30 to Zero depth at a point 36, intermediate the ends of the valve. The slot 35 is located, of course, in a position to register with port 30 as the piston approaches the end of its stroke.

An additional means of accomplishing the same result is shown in the modified slide valve of FIG. 6. In this case the metering slot 41 is of either constant or decreasing depth, but gradually decreases in width from one end to a point intermediate its ends. A third means (not shown) includes a series of aligned holes drilled through the sleeve or valve body, and of gradually decreasing diameter. Alternatively, the mentioned slots may extend throughout the length of the valve, if desired.

conventionally cylinder is provided with a combination internal piston stop 39 (FIG. 5) and cylinder head 31 which is provided with seals 32 and 33, and which is fixed in the end of the cylinder by a snap ring 34, or by other suitable means. The stop portion 39 of the head is not essential to my invention but is desirable.

Operational environment While no motive fluid control valve is shown in the drawings, it will be assumed that a suitable valve is interposed in the hydraulic actuating system to selectively direct motive fiuid through port 30 into the right hand end of cylinder 10, and to selectively direct used fluid from that end of the cylinder outward through port 30 to the system reservoir.

To better illustrate the results produced by the described invention, it will also be assumed that the piston rod 11 is connected to selectively lift an extremely heavy load, such as the boom and loaded bucket of a mechanical shovel or back hose, and to drop the boom and its bucket into the excavation after the loaded bucket has been dumped. This dropping action places the entire load of the boom and bucket on the fluid being discharged from the cylinder. The load being dropped acquires a terrific kinetic energy force which must be dissipated by a progressive deceleration of piston travel only near the extreme end of its permitted stroke, without building up an excessive fluid pressure within the cylinder. The described invention accomplishes this desired result in the following manner.

Operation The dropped load is applied to the piston rod 11 in the direction indicated by the arrow 40, FIG. 1, after the control valve has been opened to discharge fluid through port 30. As a result piston 22 begins to travel to the right, its rate of travel accelerating rapidly.

Spring maintains valve 14 in slidable contact with thot portion of the cylinder wall which is in longitudinal alignment with port 30, as illustrated in FIG.-3. Internal pressure in the cylinder chamber ahead of the piston begins to increase because the piston is attempting to force fluid out of the cylinder faster than it can flow through port 30. At a certain point in piston travel, depending on the degree of pressure build up, port 30 begins to'act as a flow restricting orifice and this action begins to prevent further piston acceleration and to absorb some of the kinetic energy of the dropping load. The metering of fluid through port 30 establishes a lower pressure at the outer end of port 30 than exists in the cylinder chamber 37, ahead of the piston. The higher pressure in chamber 37 results in an unbalanced hydraulic force which is applied to the inner surface of the valve, in the direction indicated by the arrows 43 (FIGS. 3 and 4). This unbalanced force thus aids spring 20 in maintaining a firm sliding contact between the valve and the adjacent cylinder wall surface.

As the piston and its slide valve 14 reach the positions shown in FIG. 4, the slot 35 begins to act as a means for progressively reducing the rate of fluid escape through orifice 30, and maintains the pressure in thechamber ahead of the piston at a substantially constant value as the travel of the piston and its rod is slowed down. Except for very minor slip flow, groove 35 constitutes the only path of flow for fluid being discharged from the cylinder, after the valve 14 has reached its FIG. 4 position.

By the time valve 14 reaches its FIG. 5 position and. washer 13 contacts the end of stop 39, the kinetic energy of the load has been completely dissipated or absorbed by the cushioning effect of the escaping fluid, the motion: of the plunger has ceased, the impact force of the piston against the stop 39 is practically nil, and the internal pressure in the cylinder between the piston and the cylinder head 31 has dropped to zero.

The operator may immediately shift the control valve to admit motive fluid through port 30 to again lift the load. Fluid pressure is directed against valve 14 in its FIG. 5 position, and bodily moves the valve laterally in the cylinder against the relatively weak action of spring 20. This valve movement uncovers port 30 and afiords ample unrestricted flow area for fluid to reach chamber 37.

To those familiar with this art it will be understood that any piston can be similarly fitted with two oppositely directed valves such as valve 14, and thus provide a cushioned stop for the piston at both ends of its stroke in a double acting working cylinder. The invention is not, therefore, limited to use in conjunction with any specific type of working cylinder or piston.

A modified form of fluid metering valve 44 is illustrated in FIG. 6. Instead of being in the form of a complete sleeve, as is the valve 14, it has a ring 45 with an internal shoulder 46, which corresponds to the shoulder 15 of valve 14. It includes only an integral elongated sleeve sector 47, the external surface of which is provided with a tapered width metering slot 41.

In valve 44, since a major portion of the sleeve has been omitted, the outer surface of sector 47 is preferably fully complemental to the interior of the portion of the cylinder Wall along which it slides. The ring 45 is of smaller exterior diameter than the interior diameter of the cylinder to afford lateral movement for the sector 47 awayfrom port 30.

Valve 44 is mounted on the piston and rod assembly in the same manner as valve 14, and functions in the same manner as valve 14.

Having described the invention With suflicient clarity to enable those familiar with this art to construct and use it, I claim:

1. Cushion stop mechanism for a piston and rod assembly which is reciprocable in a closed cylinder which has a side Wall port near one of its ends to admit and discharge fluid from the cylinder, comprising:

an elongated slide valve carried by the piston and rod assembly within the cylinder, and having a longitudinally disposed elongated surface shaped and positioned to slidably contact and cooperate with the cylinder wall surface surrounding the port to progressively decrease the volume flow of fluid outward through said port as the piston approaches that end of its stroke nearest the port;

said slide valve having limited transverse movement with respect to the piston and toward and away from that portion of the cylinder wall surface adjacent said port, and when the valve is covering said port it is responsive to fluid under pressure introduced through the port to move bodily away from the port to afford free entry for incoming fluid;

and means resiliently urging the valve into cylinder Wall contacting relationship.

2. The mechanism described in claim 1 in which the port cooperating surface of the slide valve is substantially complemental in cross sectional configuration to the cross sectional configuration of that portion of the interior cylinder wall surface surrounding the port.

3. The mechanism described in claim 1, and:

an elongated recess or slot in that surface of the slide valve which slides along and cooperates with the cylinder wall surface, said recess being elongated in a direction parallel to the path of travel of the valve, and located in a osition to register with said port, said recess extending from that end of the slide valve nearest said port toward its opposite end, and progressively decreasing in cross sectional area from its port end toward its opposite end, said recess when in registry with said cylinder port serving to extend the time period during which the permitted volume flow of fluid outward through the cylinder port is progressively decreased.

4. The mechanism described in claim 1 in which the slide valve has limited transverse movement with respect to the cylinder wall surface with which it cooperates, and is responsive to fluid under pressure introduced into the cylinder through the cylinder port to move laterally away from the port entrance to afford free entry for incoming fluid;

and means resiliently urging the valve into cylinder wall contacting relationship.

5. Cushion stop mechanism for a piston and rod assembly which is reciprocable in a closed cylinder which has a side wall port near one of its ends to admit and discharge fluid from the cylinder, comprising:

an elongated slide valve within the cylinder having a longitudinally disposed elongated surface which is substantially complemental in cross sectional configuration to the cross sectional configuration of any fractional portion of the bore surface of said cylinder, said valve surface being capable of sliding longitudinally along and cooperating with the interior cylinder wall surface surrounding said port to progressively decrease the volume flow of fluid outward through the port as the piston approaches the port, said valve also being smaller in cross sectional dimension than the bore of said cylinder; and

means securing the valve to the piston and rod assembly for reciprocation therewith in a position ahead of the piston as it travels toward the port, said means normally maintaining the valve in slidable contact with that portion of the cylinder bore surface which is longitudinally aligned with the cylinder port, said means also affording limited tranverse movement of the valve away from the bore surface with which it is normally in slidable contact,

whereby as the piston approaches that end of its stroke nearest the port, the valve gradually closes the port progressively decreasing the volume flow of fluid outward from the cylinder, thereby slowing and eventually stopping piston travel, and after the valve has substantially closed the port and piston travel has stopped, the valve is moved transversely away from the port entrance in response to fluid under pressure introduced through the port to move the piston toward the opposite end of its stroke.

6. The mechanism described in claim 5 in which the means securing the valve to the piston and rod assembly includes a means resiliently urging the valve into cylinder wall contacting relationship.

7. The mechanism described in claim 5, and:

an elongated recess or slot in that surface of the slide valve which slides along and cooperates with the cylinder wall surface, said recess being elongated in a direction parallel to the path of travel of the valve, and located in a position to register with said port, said recess extending from the leading end of the slide valve toward its opposite end, and progressively decreasing in cross sectional area from its leading end toward its opposite end, said recess when in registry with said cylinder port serving to extend the time period during which the permitted volume flow of fluid outward through the cylinder port is progressively decreased.

8. The cushion stop mechanism described in claim 5 in which the means securing the valve to the piston and rod assembly includes:

a pair of aligned diametrically disposed pins, one on each side of the piston rod, the outer ends of said pins terminating short of the cylinder wall, the outer end of at least one of said pins having a sliding connection with a portion of said valve to afford limited transverse but non-rotational movement of the valve; and

means fixed on the rod and in limited contact with both said pins to maintain them in their longitudinally aligned diametrically opposed positions, and against movement about the longitudinal axis of the piston rod.

9. Cushion stop mechanism for a piston and rod assembly which is reciprocable in a closed cylinder which has a side wall port near one of its ends to admit and discharge fluid from the cylinder, comprising:

a fluid metering valve in the general form of a sleeve having a slightly lesser outside diameter than that of the cylinder bore located between the piston and said end port in a position to progressively close the end port near the end of a piston stroke;

a longitudinally disposed fluid metering groove in the peripheral surface of said valve extending from and having a gradually decreasing fluid flow area from that end of the valve nearest the end port to a point short of the opposite valve end, said groove being located to register with and to progressively restrict flow outward through said end port as the piston nears the end of a stroke;

means mounting the valve against relative rotation with respect to the piston, but affording tranverse movement of the valve within the cylinder bore along a diametral plane which intersects the fluid metering groove and said end port; and

spring means urging the valve into an eccentric position in the cylinder bore in which that portion of the valve surface which is in longitudinal alignment with the metering groove is in substantial sealing contact with the adjacent portion of the cylinder bore surface.

References Cited UNITED STATES PATENTS 894,882 8/1908 Green 92-257 2,102,040 12/ 1937 Slade 91-405 2,194,078 3/ 1940 Simonds 91-405 2,974,643 3/ 1961 Gillham et a1 91405 3,083,695 4/1963 Stiglic 91-409 3,120,157 2/ 1964 Mello 91408 FOREIGN PATENTS 905,677 9/ 1962 Great Britain.

MARTIN P. SCHWARDON, Primary Examiner.

PAUL E. MASLOUSKY, Examiner. 

1. CUSHION STOP MECHANISM FOR A PISTON AND ROD ASSEMBLY WHICH IS RECIPROCABLE IN A CLOSED CYLINDER WHICH HAS A SIDE WALL PORT NEAR ONE OF ITS ENDS TO ADMIT AND DISCHARGE FLUID FROM THE CYLINDER, COMPRISING: AN ELONGATED SLIDE VALVE CARRIED BY THE PISTON AND ROD ASSEMBLY WITHIN THE CYLINDER, AND HAVING A LONGITUDINALLY DISPOSED ELONGATED SURFACE SHAPED AND POSITIONED TO SLIDABLY CONTACT AND COOPERATE WITH THE CYLINDER WALL SURFACE SURROUNDING THE PORT TO PROGRESSIVELY DECREASE THE VOLUME FLOW OF FLUID OUTWARD THROUGH SAID PORT AS THE PISTON APPROACHES THAT END OF ITS STROKE NEAREST THE PORT; SAID SLIDE VALVE HAVING LIMITED TRANSVERSE MOVEMENT WITH RESPECT TO THE PISTON AND TOWARD AND AWAY FROM THAT PORTION OF THE CYLINDER WALL SURFACE ADJACENT SAID PORT, AND WHEN THE VALVE IS COVERING SAID PORT IT IS RESPONSIVE TO FLUID UNDER PRESSURE INTRODUCED THROUGH THE PORT TO MOVE BODILY AWAY FROM THE PORT TO AFFORD FREE ENTRY FOR INCOMING FLUID; AND MEANS RESILIENTLY URGING THE VALVE INTO CYLINDER WALL CONTACTING RELATIONSHIP. 